Exploring, drilling and completing hydrocarbon wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years, well architecture has become more sophisticated where appropriate in order to help enhance access to underground hydrocarbon reserves. For example, as opposed to wells of limited depth, it is not uncommon to find hydrocarbon wells exceeding 30,000 feet in depth. Furthermore, today's hydrocarbon wells often include deviated or horizontal sections aimed at targeting particular underground reserves. Indeed, at targeted formation locations, it is quite common for a host of lateral legs and perforations to stem from the main wellbore of the well toward a hydrocarbon reservoir into the surrounding formation.
The above described perforations are formed and effectively completed by a series of applications that begin with perforating the well wall. So, for example, a casing defining the well may be perforated by a series of projectiles directed at a targeted location by way of a perforating gun. The gun itself may be equipped with conventional charges for powering the projectiles, with the application itself directed over standard wireline running from the oilfield surface.
Perforating in this manner generally takes place in a zone by zone fashion. That is, for sake of effective management, production regions are divided into 20 to 40 or more zones, often ranging from 3 feet to 50 feet or so apiece. Thus, over the course of perforating a well, one zone is generally perforated, followed by another, and so on. Once more, fully developing perforations for sake of enhancing recovery, requires more than the initial perforating via the perforating gun. Rather, follow-on fracturing, or “fracing”, and cleanout applications are also employed. The fracturing involves pumping a fracturing fluid with solid proppant particulate to the perforated locations to provide a degree of channel stabilization. Subsequently, a cleanout application may be employed to remove excess debris and particulate following the perforating and fracturing.
Unfortunately, the step by step process of perforating, fracturing and cleanout is performed on a zone by zone basis. So, for example, following the perforating, the gun may be removed and other fracturing and cleanout equipment lowered into position for these subsequent applications. Afterwards, the entire process of delivering and removing the various pieces of equipment may be repeated for each and every zone. In fact, each zone may even be isolated in advance of perforating and fracturing, thus adding further layers of complexity and time to the overall process.
In order to streamline the above described process of perforating and fracturing various downhole zones, coiled tubing perforating equipment may be utilized. More specifically, a hydraulically driven coiled tubing assembly may be outfitted with a jetting tool and other features capable of performing each of the various perforating, fracturing and cleanout functions. That is, the coiled tubing may be advanced to the downhole perforating location and the jetting tool employed to create the above described perforations. However, rather than remove the coiled tubing, it may be left in place as a fluid-based fracturing application is directed through the coiled tubing (or adjacent to it within an annulus formed between the coiled tubing and the wellbore) to the recently perforated zone. Indeed, the coiled tubing may remain in place to serve as the platform for a subsequent circulating cleanout application.
In theory, routing each of the various applications through the same bottom hole assembly (BHA) at the end of the coiled tubing would save a tremendous amount of time in terms of trips into the well. That is, after one zone is finished, the coiled tubing may be moved to the next zone and the same applications repeated through the same BHA without the need to return to the oilfield surface.
Unfortunately, the ability to fully take advantage of the coiled tubing BHA for the different applications noted above is limited by the nozzles of the jetting tool. As noted above, the BHA is outfitted with a jetting tool which utilizes nozzles in achieving the perforating at each zone. However, even the most robust of nozzles is likely to be effective for no more than about 5 to 10 perforating applications. This is due to the naturally occurring erosion which tends to enlarge the diameter of the nozzles over repeated use. As a result, after perforating and fracturing 5 to 10 zones or so, the entire coiled tubing is removed from the well so that the nozzles and/or the entire jetting tool of the BHA may be replaced. The assembly is then re-deployed for use in subsequent zones, with this process repeated until all of the perhaps 40 or more zones are fully perforated, fractured and cleaned out. Thus, the ability to attain the full advantage leaving the coiled tubing downhole throughout the perforating and fracturing of the entire well remains elusive.
In some circumstances, efforts may be undertaken to extend the effective life of the nozzle without removing the BHA. For example, as later zones are perforated, operators at the oilfield surface may increase pressure and flow rates in an attempt to compensate for increasing diameter of the eroding nozzles. However, such efforts are unlikely to extend nozzle life beyond an additional perforating application or two. Thus, as a practical matter, the operator is still likely to remove the entire BHA on multiple occasions, adding significant time and expense to overall perforating and fracturing operations.